This invention relates to a bore hole scanner (an apparatus for observing the wall of a bore hole which, in the present invention, refers to boring holes and pipe holes and the like) for being raised, lowered and moved within a bore hole to observe the wall of the bore hole by means of a scanner incorporated in a sonde.
In drilling underground cavities for dams, tunnels and the like, a geological survey is performed at the site and the results of the survey are reflected in the design drawings. It is also necessary to select the method of executing the project and to assure perfection in terms of how the project proceeds, project safety measures and the like. In a geological survey of this kind, it is generally necessary to ascertain the cracking direction, inclination and properties of the rock, as well as the direction and dip of the bed. One method of performing such a survey is to bore a hole at the site and sample the core in order to observe its nature. Another method is to bore a hole at the site and make a direct observation of the bore hole wall. In order to execute the method that entails direct observation of the bore hole wall, various items of equipment are available such as televisions, periscopes, cameras and scanners, all for observation of the bore hole wall.
With reference to FIG. 1, there is shown an apparatus 30 for reading in a signal produced by image pick-up means provided in a sonde 32, and for generating observation information indicative of the bore hole by subjecting the signal to data processing. The apparatus 30 includes a CRT for monitoring the image of the bore hole wall, a data processor, namely a computer, a memory device such as a magnetic tape, floppy disc or magnetic disc, and an output unit such as a printer. As shown in FIG. 1(b), the sonde 32 houses the image pick-up means which produces the image of the bore hole wall. A winch 31 [FIG. 1(a)]raises and lowers the sonde 32.
With reference again to FIG. 1(b), the sonde 32 raised and lowered in the bore includes an optical head 37 coupled to a swiveling motor 33 and having a direction finder 34, a lens 35 and a mirror 36. Also provided are a light source 43 for transmitting a light beam toward the optical head 37 through a half-mirror 40, a slit 41 and a lens 42 for forming the light beam, and a slit 38 and photoelectric transducer 39 for sensing the light beam from the optical head 37 after the beam has been reflected at the bore wall surface. With an arrangement of this type, the light from the light source 43 is shaped into a beam by the slit 41 and lens 42, and the resulting light beam is projected toward the bore hole wall via the half-mirror 40, mirror 36 and lens 35. The intensity of the light beam reflected from the bore wall surface is measured by the photoelectric transducer 39 via the lens 35, mirror 36, half-mirror 40 and slit 38. While the optical head 37 is being swiveled by the swiveling motor 33, the sonde 32 is lowered within the bore hole. When this done, a bore hole wall scan of the kind shown in FIG. 2 is carried out and an electric signal corresponding to the intensity of the reflected beam is obtained from the photoelectric transducer 39.
An arrangement can be adopted in which a triangular mirror is rotated instead of the half-mirror 40, in which case the light from the light source would be reflected by one side of the triangular mirror to irradiate the bore hole wall surface, with the reflected light being introduced to the photoelectric transducer upon being reflected by another side of the triangular mirror. Such an arrangement, as disclosed, for example, in the specification of U.S. Pat. No. 4,779,201, has been put into practical use by the present inventors.
However, since the observation of the bore hole wall by the conventional bore hole scanner employs a mechanical scanning system, as described above, problems are encountered in the mechanical scanning section that involves rotational movement. Specifically, the swiveling motor 33, the direction finder 34 and the optical head 37 having the lens 35 mirror 36, all of which constitute the mechanical scanning section, sustain severe wear due to the rotational motion thereof. The maintenance required, such as replacement and adjustment, involves considerable labor and expense.